1. Field of the Invention
This invention relates to a system for identifying objects in a combined circularly scanned image and determining their location and orientation.
2. Description of the Related Art
A variety of optical and electronic image processing techniques have been developed for the purpose of automatically identifying objects in an image. Optical techniques are especially suitable for use in applications requiring real time processing of a large amount of image information. The filters and lenses used in such systems transform entire images at the speed of light, in contrast to purely electronic image processing systems which generally process image information serially, pixel by pixel.
A device known as the "spatial light modulator" (SLM) has recently become available for use in converting electronic information into optical form, using a coherent light beam as a carrier of the information. The SLM is essentially a filter whose optical characteristics are varied in response to an electrical input signal. This allows conversion of information from electronic to optical form, in a manner which optimizes the different advantages of electronic and optical systems in a combined electronic and optical image processing system.
Identification of objects in an image involves the process known as "matched filtering". This process is based upon a correlation function produced by taking the inverse Fourier transform of the Fourier transforms of an input image and a complex conjugate reference image. Various lens systems are currently available for performing the Fourier transform of image information contained in a coherent beam of light. Comparison of the images is accomplished by combining the Fourier transforms of each image. The resulting "correlation spots" are an indication of the degree of correlation between the two images. This type of optical matched filtering system is useful for comparing input images with a limited number of matched filters, but because the references images are conventionally stored in optical form, the system is much less useful in applications involving a greater number of reference images. These applications include parts retrieval systems, autonomous guidance and artificial intelligence systems for land, air and space vehicles, and surveillance systems.